The present invention relates to a feed device, and more particularly to a feed device for feeding an image recording medium such as a film or the like by gripping the same between a drive drum and nip rollers, the drive drum being operatively coupled to a rotative drive source through a plurality of speed reducer means comprising belts and pulleys, the belt which engages the drive roller being of higher rigidity than the ridigity of the other belts, so that the drive drum can accurately be rotated without being affected by external forces.
Image scanning reading and recording systems are widely used in the printing and platemaking industries for reading and electrically processing image information of originals or subjects to produce original film plates with a view to simplifying the entire process and improving the quality of printed images.
The image scanning reading and recording systems are basically constructed of an image reading apparatus, a controller, and an image recording apparatus which may be coupled to or separate from each other. In the image reading apparatus, a reflective subject or a linear image subject is scanned with a light beam, and its image information is detected by a photomultiplier or the like, or ready by a CCD (charge-coupled device) camera, so that the image information of the subject is converted into an electrical signal representing varying intensities of the reflected light from the subject. Then, the photoelectrically converted image information from the image reading apparatus is processed in the controller for signal processing such as gradation correction, edge emphasis, and the like according to platemaking conditions. Thereafter, the processed image signal from the controller is converted in the image recording apparatus into a light signal such as a laser beam signal which is applied to an image recording medium comprising a photosensitive material such as a photographic film for recording a desired image thereon. The image recording medium with the image recorded thereon is developed and will be used as a film plate for printing.
More specifically, the image recording apparatus in the image scanning reading and recording system for applying a laser beam on a film or the like based on the image information of a subject to record the image on the film or the like is constructed and operates as follows:
A magazine with a roll of elongated film stored therein is loaded in the image recording apparatus. Then, the film is gripped by a pair of feed rollers. The feed rollers are rotated to feed the film into an image scanner. In the image scanner, the film is fed in an auxiliary scanning direction by a rotating drive drum and nip rollers that can be rollingly held against the drive drum. At the same time, a laser beam that is modulated by the processed image signal from the controller is applied to the film to scan the same in a main scanning direction, thereby recording the desired image on the film. Thereafter, the film is automatically cut off into a desired length by a cutter in the image recording apparatus, and then delivered into an image developing apparatus, for example, by a film delivery system.
In order to record the desired image accurately on the film, it is necessary to feed the film highly accurately in the auxiliary scanning direction at a relatively low speed. To meet this requirement, a plurality of speed reducer means comprising belts and pulleys are disposed between a rotative drive source such as a motor or the like and the drive drum. When the rotative drive source is energized, the speed of rotation thereof is reduced by the speed reducer means, and the drive drum is rotated at the reduced speed of rotation.
The belts of the speed reducer means are made of a material having relatively low rigidity such as an elastomer like synthetic rubber or the like, or a synthetic resin material. Therefore, if the load on the drive drum fluctuates, such as when the leading end of the film while being gripped by the drive drum and the nip rollers and fed in the auxiliary scanning direction enters between the paired feed rollers, the belts of relatively low rigidity are affected by such a load fluctuation to cause the drive drum to suffer irregular rotational speeds. As a result, the film cannot accurately be fed in the auxiliary scanning direction, and thus the desired image cannot accurately be recorded on the film.
The belts of the speed reducer means may be made of a material of high rigidity such as a metalic material. Since, however, the metallic belts have a high resonant frequency, rotational fluctuations, i.e., high-frequency components of the rotational speed, of the rotative drive source tend to be transmitted through the belts to the drive drum. Consequently, the rotational speed of the drive drum is also liable to vary, and it cannot feed the film accurately in the auxiliary scanning direction at a constant speed.